Schema.org Structured Data Markup is a collection of data tags that can be added to your site to allow Search Engines to more easily interpret the content and use it to enhance Search Results. For example there are tags for providing information about your Local Business such as address and phone number, or adding product information on e-commerce pages so that these products can be displayed in shopping aggregators like Google Shopping.
It is a good idea to start incorporating some relevant Schema.org tags into your site to improve interpretation and display by Search Engines.